When you see this in a type signature it indicates that you can
pass the function a Lens, Getter,
Traversal, Fold,
Prism, Iso, or one of
the indexed variants, and it will just "do the right thing".

Most Getter combinators are able to be used with both a Getter or a
Fold in limited situations, to do so, they need to be
monomorphic in what we are going to extract with Const. To be compatible
with Lens, Traversal and
Iso we also restricted choices of the irrelevant t and
b parameters.

This is a generalized form of listen that only extracts the portion of
the log that is focused on by a Getter. If given a Fold or a Traversal
then a monoidal summary of the parts of the log that are visited will be
returned.

This is a generalized form of listen that only extracts the portion of
the log that is focused on by a Getter. If given a Fold or a Traversal
then a monoidal summary of the parts of the log that are visited will be
returned.

This is a generalized form of listen that only extracts the portion of
the log that is focused on by a Getter. If given a Fold or a Traversal
then a monoidal summary of the parts of the log that are visited will be
returned.

This is a generalized form of listen that only extracts the portion of
the log that is focused on by a Getter. If given a Fold or a Traversal
then a monoidal summary of the parts of the log that are visited will be
returned.